ABSTRACTAN EVALUATION OF OPERATIONAL EFFECTS OF CORRIDOR-WIDE ACCESS-CONTROL MODIFICATIONSByMuhammad Abrar SiddiquiHigh access densities and low corner clearances on multi-lane arterials with two-way left-turn lanes (TWLTL) have a significant detrimental effect on traffic safety and mobility. From the operational perspective, there is a wide range of criteria used by various agencies for the determination of corner clearances and access point densities. This research quantifies the operational impacts of access modifications at midblock and corner driveways on 5-lane roads with TWLTL using micro-simulation software VISSIM. The unique aspects of this research are that no major geometric changes in the corridor were made (other than signal optimization), and that modifications to corner and midblock driveways were also modeled simultaneously to evaluate their localized as well as combined effect on corridor-wide operations.By varying mainline volumes, driveway volumes, access density, access location, and access type, 136 theoretical models were developed for urban arterials based on calibrated field conditions. The TWLTL operations in VISSIM were modeled by a combination of overlapping links and connectors. `Priority rules' were used to determine the appropriate right-of-way for conflicting traffic using gap acceptance data for in- and out-bound driveway movements. It was determined that modeling TWLTL operations in VISSIM is only feasible for up to 24 midblock driveways per mile with up to 200 vehicles per hour per driveway (vphpd) so as to avoid overflow problem in the TWLTL with static routes.The operational evaluation was performed at three levels using average delay (seconds/vehicle) as the primary measure of effectiveness (MOE): corridor-wide, signalized intersections, and driveway-specific. At the corridor-level, the average delay ranged from 50.9 s/veh for the model with five signalized intersections and no driveways with low mainline volume, to 94.7 s/veh for the model with five signalized intersection and 20 corner- and 24 midblock full-access driveways with high mainline volume. At the signalized intersections, the variation in average delays between cases was found to be small, with none of the intersections in any model shifting towards a better or worse level-of-service (LOS). However, direction-specific delays did have an impact on the driveway traffic especially at corner driveways. In the evaluation of driveways, the trends in increased delays were as expected, with increasing values as the number of driveways increased especially in full-access cases. It was found that that the impact of mainline volume is much more significant on driveway operations than the impact of increased driveway density. Also, the impact of driveway volumes was more pronounced at high mainline volumes. For low to medium mainline volumes, the increase in driveway volume did not have a significant impact on driveway delays.The quantification of traffic operations from theoretical models is summarized in the form of flowcharts and corresponding case-specific results that will provide guidelines for transportation engineers and planners to determine the impact of various access management alternatives on urban arterials.
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